panel-notifications: findings of the technical and security reviews

Neither review (read-only agents, Opus and Fable, over 972a9f8..400aa76) has
a Critical finding. Both found the same serious one, and more:

- The notification about refused mail was built on what a rejected row says
  of itself. Its domain is the one in MAIL FROM, which the client typed and
  Postfix has not yet held against the login when the milter refuses: an
  application over its limit could have had the panel write a message per
  made-up domain, to another tenant's users among others. And the same
  status is written when an application is refused for its client address,
  which is no limit. Refusals are now counted by the domain the login is
  registered under, only for logins that exist and only while a limit is set
  on the login or its domain; one subject per sending domain. They are read
  through a partial index of their own (migration 0005): the query walked
  the whole send log every minute.
- Account and user e-mails were checked with the DMARC report validator,
  which refuses Gmail and the like - the owner's own kind of address. A new
  validate.AccountEmail accepts them and refuses a local part beginning "-".
- "Said" now means sent: what arises while nobody can be told, or while
  Postfix does not take the message, is told at a later check. Its ending
  with nobody left to tell is simply over.
- Two DNS checks must be 45 minutes apart as well as two: the last check
  before a restart and the first after it were minutes apart.
- The notifier's own mail waiting in the queue, and its bounce coming back
  to postmaster@ this server, are not the queue's subject. A listing cut at
  its size limit or with a line too long to read is no listing; postqueue -j
  gets 30 seconds.
- The tables must name the selector the panel shows, not only have the line.
- An a/mx lookup that did not answer inside the SPF check made the record
  "not authorising"; it is "cannot tell" now, for the pages too.
- A ceiling of 60 messages an hour; a pass stops between domains when the
  process is asked to stop; sendmail gets a WaitDelay; days are rounded as a
  person counts; a failed read of the switch shows it on, not off.

Recorded as accepted in security.md, with a roadmap candidate
(from-header-binding): an application can have a message signed as the
server's own name - or, as always, as another registered domain - by writing
it into the From: header, which nothing holds against the login.

Left as found: a recipient whose copy failed while another's went out is not
tried again; a certificate that lives under 14 days is reported at each
renewal.

On the test server, for this tree: go vet clean, go test ./... 23 packages
ok, make e2e ok (326 s).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plans/panel-notifications.md

@@ -80,7 +80,7 @@ A background check once an hour for DNS, certificate and queue.
 |---|---|---|
 | DNS mismatch | after two checks in a row found it (it has held for an hour). A resolver that did not answer is not a mismatch | after two good checks in a row |
 | Certificate | 14 days before expiry, and again 3 days before if it is still the same certificate | none |
-| Level-2 limit refused mail | at the first refusal for a domain or application, then at most once a day for the same limit | none |
+| Level-2 limit refused mail | at the first refusal of a sending domain's applications, then at most once a day for that domain (one subject per domain, as built: what the refused row says of its domain is the client's own word, so the registry is asked) | none |
 | Queue older than three days | when such a message appears | one, when none is left |
 
 Event state is kept in the database, so a restart announces nothing a second
@@ -115,5 +115,5 @@ to the owner before any code ([panel-redesign.md](panel-redesign.md)
 - [x] Panel: Account, Settings, Health card, help
 - [x] guide.md, architecture.md, security.md, schema-migrations.md
 - [x] `go vet`, `go test`, e2e: a level-2 refusal reaches a mailbox as a signed notification (on the test server: vet ok, 23 packages ok, e2e ok; "once" and "clears" are held by the unit tests of `internal/notify`)
-- [ ] Technical review
-- [ ] Security review
+- [x] Technical review — **Opus** (2026-10-12; no Critical. Fixed: refusals counted by the registered domain and only under a limit, with an index of their own; account e-mails may be at public mail hosts; "said" means sent; DNS checks must be 45 minutes apart; the notifier's own mail is not a queue subject and a cut or unreadable listing is no listing; the tables must name the selector the panel shows; an unanswered `a`/`mx` lookup is not an SPF mismatch; a pass stops between domains at shutdown; days are rounded as a person counts. Left as found: a recipient whose copy failed while another's went out is not retried; a certificate that lives under 14 days is reported at each renewal)
+- [x] Security review — **Fable** (2026-10-12; no Critical. Fixed: the limit notification was built on the domain a client writes in `MAIL FROM` - a mail cannon and a way to write to another tenant's users; a ceiling of 60 messages an hour; [security.md](../security.md) corrected on who can submit locally and on what the account e-mail now is. Recorded as accepted, with a roadmap candidate: an application can have a message signed as the server by writing its name into `From:` - the header is not held against the login, for sending domains either)